Amazon EBS Volume Types

Amazon EBS provides the following volume types, which differ in performance characteristics
and
price, so that you can tailor your storage performance and cost to the needs of your
applications. The volumes types fall into two categories:

Throughput-oriented storage for large volumes of data that is infrequently
accessed

Scenarios where the lowest storage cost is important

Cannot be a boot volume

API Name

gp2

io1

st1

sc1

Volume Size

1 GiB - 16 TiB

4 GiB - 16 TiB

500 GiB - 16 TiB

500 GiB - 16 TiB

Max. IOPS**/Volume

10,000

20,000

500

250

Max. Throughput/Volume†

160 MiB/s

320 MiB/s

500 MiB/s

250 MiB/s

Max. IOPS/Instance

75,000

75,000

75,000

75,000

Max. Throughput/Instance

1,750 MB/s

1,750 MB/s

1,750 MB/s

1,750 MB/s

Dominant Performance Attribute

IOPS

IOPS

MiB/s

MiB/s

*Default volume type

**gp2/io1 based on 16 KiB I/O size, st1/sc1 based on 1 MiB I/O size

† To achieve this throughput, you must have an instance that supports it, such as
r3.8xlarge or x1.32xlarge.

The following table describes previous-generation EBS volume types. If you need higher
performance or performance consistency than previous-generation volumes can provide,
we
recommend that you consider using General Purpose SSD (gp2) or other current volume types. For more
information, see Previous Generation
Volumes.

There are several factors that can affect the performance of EBS volumes, such as
instance
configuration, I/O characteristics, and workload demand. For more information about
getting
the most out of your EBS volumes, see Amazon EBS Volume Performance on Windows Instances.

General Purpose SSD (gp2) Volumes

General Purpose SSD (gp2) volumes offer cost-effective storage that is ideal for a broad range of
workloads. These volumes deliver single-digit millisecond latencies and the ability
to burst
to 3,000 IOPS for extended periods of time. Between a minimum of 100 IOPS (at 33.33
GiB and below) and a maximum of 10,000 IOPS (at 3,334 GiB and above), baseline
performance scales linearly at 3 IOPS per GiB of volume size. AWS designs gp2 volumes to
deliver the provisioned performance 99% of the time. A gp2 volume can range in size from 1
GiB to 16 TiB.

I/O Credits and Burst Performance

The performance of gp2 volumes is tied to volume size, which determines the baseline
performance level of the volume and how quickly it accumulates I/O credits; larger
volumes
have higher baseline performance levels and accumulate I/O credits faster. I/O credits
represent the available bandwidth that your gp2 volume can use to burst large amounts of
I/O when more than the baseline performance is needed. The more credits your volume
has
for I/O, the more time it can burst beyond its baseline performance level and the
better
it performs when more performance is needed. The following diagram shows the burst-bucket
behavior for gp2.

Each volume receives an initial I/O credit balance of 5.4 million I/O credits, which
is enough to sustain the maximum burst performance of 3,000 IOPS for 30 minutes. This
initial credit balance is designed to provide a fast initial boot cycle for boot volumes
and to provide a good bootstrapping experience for other applications. Volumes earn
I/O
credits at the baseline performance rate of 3 IOPS per GiB of volume size. For example,
a
100 GiB gp2 volume has a baseline performance of 300 IOPS.

When your volume requires more than the baseline performance I/O level, it draws on
I/O credits in the credit balance to burst to the required performance level, up to
a
maximum of 3,000 IOPS. Volumes larger than 1,000 GiB have a baseline performance that
is
equal or greater than the maximum burst performance, and their I/O credit balance
never
depletes. When your volume uses fewer I/O credits than it earns in a second, unused
I/O
credits are added to the I/O credit balance. The maximum I/O credit balance for a
volume
is equal to the initial credit balance (5.4 million I/O credits).

The following table lists several volume sizes and the associated baseline performance
of the volume (which is also the rate at which it accumulates I/O credits), the burst
duration at the 3,000 IOPS maximum (when starting with a full credit balance), and
the
time in seconds that the volume would take to refill an empty credit balance.

Volume size (GiB)

Baseline performance (IOPS)

Maximum burst duration @ 3,000 IOPS (seconds)

Seconds to fill empty credit balance

1

100

1862

54,000

100

300

2,000

18,000

214 (Min. size for max. throughput)

642

2,290

8,412

250

750

2,400

7,200

500

1,500

3,600

3,600

750

2,250

7,200

2,400

1,000

3,000

N/A*

N/A*

3,334 (Min. size for max. IOPS)

10,000

N/A*

N/A*

16,384 (16 TiB, max. volume size)

10,000

N/A*

N/A*

* Bursting and I/O credits are only relevant to volumes under 1,000 GiB, where burst
performance exceeds baseline performance.

The burst duration of a volume is dependent on the size of the volume, the burst IOPS
required, and the credit balance when the burst begins. This is shown in the following
equation:

If your gp2 volume uses all of its I/O credit balance, the maximum IOPS
performance of the volume remains at the baseline IOPS performance level (the rate
at
which your volume earns credits) and the volume's maximum throughput is reduced to
the
baseline IOPS multiplied by the maximum I/O size. Throughput can never exceed 160
MiB/s.
When I/O demand drops below the baseline level and unused credits are added to the
I/O
credit balance, the maximum IOPS performance of the volume again exceeds the baseline.
For example, a 100 GiB gp2 volume with an empty credit balance has a baseline
performance of 300 IOPS and a throughput limit of 75 MiB/s (300 I/O operations per
second * 256 KiB per I/O operation = 75 MiB/s). The larger a volume is, the greater
the
baseline performance is and the faster it replenishes the credit balance. For more
information about how IOPS are measured, see I/O Characteristics.

If you notice that your volume performance is frequently limited to the baseline level
(due to an empty I/O credit balance), you should consider using a larger gp2 volume
(with a higher baseline performance level) or switching to an io1 volume for workloads
that require sustained IOPS performance greater than 10,000 IOPS.

Throughput Performance

The throughput limit for gp2 volumes is 128 MiB/s for volumes less than or equal to
170 GiB and 160 MiB/s for volumes over 170 GiB.

Provisioned IOPS SSD (io1) Volumes

Provisioned IOPS SSD (io1) volumes are designed to meet the needs of I/O-intensive workloads,
particularly database workloads, that are sensitive to storage performance and consistency.
Unlike gp2, which uses a bucket and credit model to calculate performance, an io1 volume
allows you to specify a consistent IOPS rate when you create the volume, and Amazon
EBS delivers
within 10 percent of the provisioned IOPS performance 99.9 percent of the time over
a given
year.

An io1 volume can range in size from 4 GiB to 16 TiB and you can provision 100 up to
20,000 IOPS per volume. The maximum ratio of provisioned IOPS to requested volume
size
(in GiB) is 50:1. For example, a 100 GiB volume can be provisioned with up to 5,000
IOPS.
Any volume 400 GiB in size or greater allows provisioning up to the 20,000 IOPS
maximum.

The throughput limit of io1 volumes is 256 KiB for each IOPS provisioned, up to a
maximum of 320 MiB/s (at 1,280 IOPS).

Your per-I/O latency experience depends on the IOPS provisioned and your workload
pattern. For the best per-I/O latency experience, we recommend that you provision
an
IOPS-to-GiB ratio greater than 2:1. For example, a 2,000 IOPS volume should be smaller
than
1,000 GiB.

Note

Some AWS accounts created before 2012 might have access to Availability Zones in
us-west-1 or ap-northeast-1 that do not support Provisioned IOPS SSD (io1) volumes. If
you are unable to create an io1 volume (or launch an instance with an io1
volume in its block device mapping) in one of these regions, try a different Availability
Zone in the region. You can verify that an Availability Zone supports io1 volumes
by creating a 4 GiB io1 volume in that zone.

Throughput Optimized HDD (st1) Volumes

Throughput Optimized HDD (st1) volumes provide low-cost magnetic storage that defines performance
in terms of throughput rather than IOPS. This volume type is a good fit for large,
sequential workloads such as Amazon EMR, ETL, data warehouses, and log processing.
Bootable st1
volumes are not supported.

Throughput Optimized HDD (st1) volumes, though similar to Cold HDD (sc1) volumes, are designed to support
frequently accessed data.

Note

This volume type is optimized for workloads involving large, sequential I/O, and we
recommend that customers with workloads performing small, random I/O use gp2. For more
information, see Inefficiency of Small Read/Writes on
HDD.

Throughput Credits and Burst Performance

Like gp2, st1 uses a burst-bucket model for performance. Volume size determines
the baseline throughput of your volume, which is the rate at which the volume accumulates
throughput credits. Volume size also determines the burst throughput of your volume,
which
is the rate at which you can spend credits when they are available. Larger volumes
have
higher baseline and burst throughput. The more credits your volume has, the longer
it can
drive I/O at the burst level.

The following diagram shows the burst-bucket behavior for st1.

Subject to throughput and throughput-credit caps, the available throughput of an st1
volume is expressed by the following formula:

(Volume size) x (Credit accumulation rate per TiB) = Throughput

For a 1-TiB st1 volume, burst throughput is limited to 250 MiB/s, the bucket fills
with credits at 40 MiB/s, and it can hold up to 1 TiB-worth of credits.

Larger volumes scale these limits linearly, with throughput capped at a maximum of
500
MiB/s. After the bucket is depleted, throughput is limited to the baseline rate of
40
MiB/s per TiB.

On volume sizes ranging from 0.5 to 16 TiB, baseline throughput varies from 20 to
a
cap of 500 MiB/s, which is reached at 12.5 TiB as follows:

40 MiB/s
12.5 TiB x ---------- = 500 MiB/s
1 TiB

Burst throughput varies from 125 MiB/s to a cap of 500 MiB/s, which is reached at
2
TiB as follows:

250 MiB/s
2 TiB x ---------- = 500 MiB/s
1 TiB

The following table states the full range of base and burst throughput values for
st1:

Volume Size (TiB)

ST1 Base Throughput (MiB/s)

ST1 Burst Throughput (MiB/s)

0.5

20

125

1

40

250

2

80

500

3

120

500

4

160

500

5

200

500

6

240

500

7

280

500

8

320

500

9

360

500

10

400

500

11

440

500

12

480

500

12.5

500

500

13

500

500

14

500

500

15

500

500

16

500

500

The following diagram plots the table values:

Note

When you create a snapshot of a Throughput Optimized HDD (st1) volume, performance may drop
as far as the volume's baseline value while the snapshot is in progress.

Cold HDD (sc1) Volumes

Cold HDD (sc1) volumes provide low-cost magnetic storage that defines performance in
terms of throughput rather than IOPS. With a lower throughput limit than st1, sc1 is a
good fit ideal for large, sequential cold-data workloads. If you require infrequent
access
to your data and are looking to save costs, sc1 provides inexpensive block storage.
Bootable sc1 volumes are not supported.

Cold HDD (sc1) volumes, though similar to Throughput Optimized HDD (st1) volumes, are designed to support
infrequently accessed data.

Note

This volume type is optimized for workloads involving large, sequential I/O, and we
recommend that customers with workloads performing small, random I/O use gp2. For more
information, see Inefficiency of Small Read/Writes on
HDD.

Throughput Credits and Burst Performance

Like gp2, sc1 uses a burst-bucket model for performance. Volume size determines
the baseline throughput of your volume, which is the rate at which the volume accumulates
throughput credits. Volume size also determines the burst throughput of your volume,
which
is the rate at which you can spend credits when they are available. Larger volumes
have
higher baseline and burst throughput. The more credits your volume has, the longer
it can
drive I/O at the burst level.

Subject to throughput and throughput-credit caps, the available throughput of an sc1
volume is expressed by the following formula:

(Volume size) x (Credit accumulation rate per TiB) = Throughput

For a 1-TiB sc1 volume, burst throughput is limited to 80 MiB/s, the bucket fills
with credits at 12 MiB/s, and it can hold up to 1 TiB-worth of credits.

Larger volumes scale these limits linearly, with throughput capped at a maximum of
250
MiB/s. After the bucket is depleted, throughput is limited to the baseline rate of
12
MiB/s per TiB.

On volume sizes ranging from 0.5 to 16 TiB, baseline throughput varies from 6 MiB/s
to
a maximum of 192 MiB/s, which is reached at 16 TiB as follows:

12 MiB/s
16 TiB x ---------- = 192 MiB/s
1 TiB

Burst throughput varies from 40 MiB/s to a cap of 250 MiB/s, which is reached at 3.125
TiB as follows:

80 MiB/s
3.125 TiB x ----------- = 250 MiB/s
1 TiB

The following table states the full range of base and burst throughput values for
sc1:

Volume Size (TiB)

SC1 Base Throughput (MiB/s)

SC1 Burst Throughput (MiB/s)

0.5

6

40

1

12

80

2

24

160

3

36

240

3.125

37.5

250

4

48

250

5

60

250

6

72

250

7

84

250

8

96

250

9

108

250

10

120

250

11

132

250

12

144

250

13

156

250

14

168

250

15

180

250

16

192

250

The following diagram plots the table values:

Note

When you create a snapshot of a Cold HDD (sc1) volume, performance may drop
as far as the volume's baseline value while the snapshot is in progress.

Magnetic (standard)

Magnetic volumes are backed by magnetic drives and are suited for workloads where
data
is accessed infrequently, and scenarios where low-cost storage for small volume sizes
is
important. These volumes deliver approximately 100 IOPS on average, with burst capability
of
up to hundreds of IOPS, and they can range in size from 1 GiB to 1 TiB.

Note

Magnetic is a Previous Generation Volume. For new applications, we recommend using
one of the newer volume types. For more information, see Previous Generation
Volumes.

Performance Considerations When Using HDD
Volumes

For optimal throughput results using HDD volumes, plan your workloads with the following
considerations in mind.

Throughput Optimized HDD vs. Cold HDD

The st1 and sc1 bucket sizes vary according to volume size, and a full bucket
contains enough tokens for a full volume scan. However, larger st1 and sc1 volumes
take longer for the volume scan to complete due to per-instance and per-volume throughput
limits. Volumes attached to smaller instances are limited to the per-instance throughput
rather than the st1 or sc1 throughput limits.

Both st1 and sc1 are designed for performance consistency of 90% of burst
throughput 99% of the time. Non-compliant periods are approximately uniformly distributed,
targeting 99% of expected total throughput each hour.

The following table shows ideal scan times for volumes of various size, assuming full
buckets and sufficient instance throughput.

In general, scan times are expressed by this formula:

Volume size
------------- = Scan time
Throughput

For example, taking the performance consistency guarantees and other optimizations
into account, an st1 customer with a 5-TiB volume can expect to complete a full volume
scan in 2.91 to 3.27 hours.

* These scan times assume an average queue depth (rounded to the nearest whole
number) of four or more when performing 1 MiB of sequential I/O.

Therefore if you have a throughput-oriented workload that needs to complete scans
quickly (up to 500 MiB/s), or requires several full volume scans a day, use st1. If you
are optimizing for cost, your data is relatively infrequently accessed, and you don’t
need
more than 250 MiB/s of scanning performance, then use sc1.

Inefficiency of Small Read/Writes on
HDD

The performance model for st1 and sc1 volumes is optimized for sequential I/Os,
favoring high-throughput workloads, offering acceptable performance on workloads with
mixed IOPS and throughput, and discouraging workloads with small, random I/O.

For example, an I/O request of 1 MiB or less counts as a 1 MiB I/O credit. However,
if
the I/Os are sequential, they are merged into 1 MiB I/O blocks and count only as a
1 MiB
I/O credit.

Limitations on per-Instance Throughput

Throughput for st1 and sc1 volumes is always determined by the smaller of the
following:

Throughput limits of the volume

Throughput limits of the instance

As for all Amazon EBS volumes, we recommend that you select an appropriate EBS-optimized
EC2 instance in order to avoid network bottlenecks. For more information, see Amazon EBS-Optimized Instances.

Monitoring the Burst Bucket Balance for gp2, st1,
and sc1 Volumes

You can monitor the burst-bucket level for gp2, st1, and sc1 volumes using the EBS
BurstBalance metric available in Amazon CloudWatch. This metric shows the percentage
of I/O credits (for gp2) or throughput credits (for st1 and sc1) remaining in the
burst bucket. For more information about the BurstBalance metric and other
metrics related to I/O, see I/O
Characteristics and Monitoring. CloudWatch also allows you to set an alarm that notifies
you when the BurstBalance value falls to a certain level. For more information,
see Creating Amazon CloudWatch
Alarms.